字节数组的 Java 比较器（字典）
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Java Comparator for byte array (lexicographic)
提问by marcorossi
I have a hashmap with byte[] keys. I'd like to sort it through a TreeMap.
我有一个带有 byte[] 键的哈希图。我想通过 TreeMap 对其进行排序。
What is the most effective way to implement the comparator for lexicographic order?
实现字典顺序比较器的最有效方法是什么？
回答by ColinD
Using Guava, you can use either of:
使用Guava，您可以使用以下任一项：
The UnsignedBytescomparator appears to have an optimized form using Unsafethat it uses if it can. Comments in the code indicate that it may be at least twice as fast as a normal Java implementation.
该UnsignedBytes比较器似乎具有使用优化的形式Unsafe，它采用，如果它可以。代码中的注释表明它可能至少是普通 Java 实现的两倍。
回答by marcorossi
Found this nice piece of code in Apache Hbase:
在 Apache Hbase 中找到了这段不错的代码：
public int compare(byte[] left, byte[] right) {
for (int i = 0, j = 0; i < left.length && j < right.length; i++, j++) {
int a = (left[i] & 0xff);
int b = (right[j] & 0xff);
if (a != b) {
return a - b;
}
}
return left.length - right.length;
}
回答by Julius Musseau
I'm assuming the problem is just with the "byte vs. byte" comparison. Dealing with the arrays is straightforward, so I won't cover it. With respect to byte vs. byte, my first thought is to do this:
我假设问题仅在于“字节与字节”的比较。处理数组很简单，所以我不会介绍它。关于字节与字节，我的第一个想法是这样做：
public class ByteComparator implements Comparator<byte> {
public int compare(byte b1, byte b2) {
return new Byte(b1).compareTo(b2);
}
}
But that won't be lexicographic: 0xFF (the signed byte for -1) will be considered smaller than 0x00, when lexicographically it's bigger. I think this should do the trick:
但这不会是按字典顺序排列的：0xFF（-1 的有符号字节）将被认为小于 0x00，当按字典顺序排列时它更大。我认为这应该可以解决问题：
public class ByteComparator implements Comparator<byte> {
public int compare(byte b1, byte b2) {
// convert to unsigned bytes (0 to 255) before comparing them.
int i1 = b1 < 0 ? 256 + b1 : b1;
int i2 = b2 < 0 ? 256 + b2 : b2;
return i2 - i1;
}
}
Probably there is something in Apache's commons-lang or commons-math libraries that does this, but I don't know it off hand.
Apache 的 commons-lang 或 commons-math 库中可能有一些东西可以做到这一点，但我不知道。
回答by Peter Lawrey
You can use a comparator which comares the Character.toLowerCase() of each of the bytes in the array (Assuming the byte[] is in ASCII) if not you will need to do the character decoding yourself or use new String(bytes, charSet).toLowerCase()but this is not likely to be efficient.
您可以使用比较器，它对数组中每个字节的 Character.toLowerCase() 进行比较（假设 byte[] 是 ASCII），如果不是，您将需要自己进行字符解码或使用，new String(bytes, charSet).toLowerCase()但这不太可能高效。
